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The purpose of coatings on implants is to achieve some or all of the improvements in biocompatibility, bioactivity, and increased protection from the release of harmful or unnecessary metal ions. During the last decade, there has been substantially increased interest in nanomaterials in biomedical science and dentistry. Nanocomposites can be described as a combination of two or more nanomaterials. By this approach, it is possible to manipulate mechanical properties, such as strength and modulus of the composites, to become closer to those of natural bone. This is feasible with the help of secondary substitution phases. Currently, the most common composite materials used for clinical applications are those selected from a handful of available and well-characterized biocompatible ceramics and natural and synthetic polymers. This approach is currently being explored in the development of a new generation of nanocomposite coatings with a wider range of oral and dental applications to promote osseointegration. The aim of this review is to give a brief introduction into the new advances in calcium phosphate nanocoatings and their composites, with a range of materials such as bioglass, carbon nanotubes, silica, ceramic oxide, and other nanoparticles being investigated or used in dentistry. [ABSTRACT FROM PUBLISHER]

Background: Until recently, very few papers have been published concerning the development, analysis and experimental verification of three-dimensional, finite element modelling of the human adult edentulous mandible. The purpose of this study was to improve the method of modelling by using computer-aided engineering (CAB) and computer- aided design (CAD) methods and to utilize the model in analyzing maxillofacial problems. Methods: The model geometry was derived from position measurements taken from 28 diamond blade cut cross-sections of an average size human adult edentulous mandible and generated using a special sequencing method. Data on anatomical, structural, functional aspects and material properties were obtained from measurements and published data. The materials were idealized as transversely isotropic. The complete model consisted of 258 solid elements and 1635 nodes. Results: The model was solved for displacements and stresses during clenching. In general, the observed displacement and stresses (tensile and compressive) were highest around the condylar region. Compressive stress was also observed around the premolar and molar bite points. Conclusion: This investigation has shown that the use of computer-aided modelling in conjunction with the finite element analysis could be effectively utilized in biomechanical analysis of the mandible. It could help to investigate many functional problems and could reduce the time of extensive experimentations. [ABSTRACT FROM AUTHOR]

31P nuclear magnetic resonance (NMR) spectroscopy was used to determine the structure of the intermediate species of sol derived from triethyl phosphite, calcium diethoxide and acetic acid. NMR spectral data revealed that the reaction proceeds via a dialkyl phosphite intermediate. The use of a dialkyl phosphite precursor (diethyl phosphite) with calcium diethoxide eliminated the aging time required in triethylphosphite method and offered an effective sol-gel procedure for monophasic hydroxyapatite. [ABSTRACT FROM AUTHOR]

Zirconia-alumina multilayer nanolaminate coatings were applied on stainless steel 316 substrates by a sol-gel dipping method. The coatings were characterised using X-ray diffraction, optical and scanning electron microscopy. The hardness and elastic modulus, the wear resistance and the oxidation resistance of the coatings were measured and assessed. It was observed that the coatings possessed fine grains, fine pores and high retention of tetragonal zirconia phase. The coatings exhibited high hardness and elastic modulus as well as good resistance to oxidation at high temperatures. However, these properties may be influenced by the interactions at the coating/substrate interface. [ABSTRACT FROM AUTHOR]

Sol-gel technology offers an alternative technique for producing bioactive surfaces for improved bone attachment. Previous work indicated that monophasic hydroxyapatite coatings were difficult to produce. In the present work hydroxyapatite was synthesized using the sol-gel technique with alkoxide precursors and the solution was allowed to age up to seven days prior to coating. It was found that, similar to the wet-chemical method of hydroxyapatite powder synthesis, an aging time is required to produce a pure hydroxyapatite phase. A methodology that has been successfully used to produce nanocrystalline hydroxyapatite thin film coatings via the sol-gel route on various substrates including alumina, Vycor glass, partially stabilized zirconia, Ti–6Al–4V alloy and single crystal MgO is described. Coatings produced on MgO substrates were characterized by X-ray diffraction and atomic force microscopy, while the analogous gels were examined with thermogravimetric and differential thermal analyses. The coatings were crack free and the surface was covered with small grains, of approximately 200 nm in size for samples fired to 1000 °C. Coating thickness varied between 70 and 1000 nm depending on the number of applied layers. [ABSTRACT FROM AUTHOR]

Stoichiometric and silica-rich mullite gels and powders were prepared using four different sol-gel methods. Thermal analysis, X-ray powder diffraction and dilatometry techniques were used to investigate the thermal decomposition, crystallisation and sintering of these mullite precursor gels. The method of preparation, by controlled hydrolysis of various mixtures of tetraethylorthosilicate, aluminium sec-butoxide and aluminium nitrate, affected the texture of the gels, producing single-phase or diphasic samples. The crystallisation sequence of the gels depended on the composition and method of preparation. Single phase mullite crystallised from homogeneous gels at 980°C, while diphasic gels initially formed of a mixture of γ-Al2O3 spinel and mullite, or simple γ-Al2O3 spinel, which subsequently transformed to mullite at 1260°C. Dilatometry and density measurement were used to investigate the sintering of compacts formed by pressing powders prepared from gels precalcined at 500°C. Varying the heating rates from 2 to 10°C min-1 had little effect on the densification to 1500°C. However, the densification rate was sensitive to the degree of crystallinity and the amount and type of phases present at the sintering temperature. The presence of γ-Al2O3 spinel in the structure initially promoted densification, but the sintering rate was reduced considerably after mullite crystallised. Diphasic materials, especially those with an excess amount of silica in the original gel, sintered to higher densities due to the presence of excess silica promoting densification by viscous phase sintering. [ABSTRACT FROM AUTHOR]